It is known to transfer information on a printing place suitable for offset printing directly from electronically stored information. The printing plate may be separate from or on a printing cylinder. For example, such information which may contain printed texts, drawings, figures, images or pictures, can be transferred to an anodized aluminum plate which has a hydrophilic surface. In accordance with the image to be printed or to be transferred, organic substances which are ink-accepting, or oleophilic, are transferred on portions of the printing plate surface by an image transfer unit, in accordance with digitally controlled image information. Particles which are transferred to the plate have oleophilic characteristics, to thereby mark the portions which are to be inked. The previously hydrophilic surface of the plate is then, where ink is to be transferred, rendered hydrophobic.
The referenced U.S. Pat. No. 5,045,697, Schneider, discloses a method and system which utilizes a thermal transfer process for transferring image information. Other arrangements and systems may be used, for example ink jet applicators or electrostatic application of particles. The printing form can be a printing plate, preferably an anodized, hydrophilic aluminum plate, or a printing cylinder having an outer jacket which has hydrophilic characteristics. The printing cylinder may have a Jacket made of ceramic, preferably Al.sub.2 O.sub.3, as well as Cr.sub.2 O.sub.3, ZrSiO.sub.4, or an aluminum-magnesium silicate; it may, also, be a ceramic or glass cylinder, which can be massive, for example.
Directly imaged printing forms have to be capable of being re-used frequently. This requires that an imaged form should be capable of being regenerated, that is, the image once applied to the printing form, after printing, must be removed, or erased therefrom, so that a new printing image can be applied. Thus, the entire printing surface, after printing of a first image, must again be rendered hydrophilic over its entire circumference.
Cleaning methods well known from surface technology frequently have the disadvantage that cleaning has to be carried out in multiple stages or steps, and that the material is mechanically or abrasively stressed. Aluminum surface, in particular, when used as printing plates and which are to be rendered hydrophilic throughout the entire surface require a plurality of method steps, which is expensive. Some of the cleaning materials, additionally, cause problems in regeneration or disposal, for recycling in an environmentally acceptable manner.